1. Field of the Invention
This invention relates to recombinant DNA methods of preparing an antibody with human tumor antigen specificity, genetic sequences coding therefor, as well as methods of obtaining such sequences.
2. Background Art
The application of cell-to-cell fusion for the production of monoclonal antibodies by Kohler and Milstein (Nature (London), 256:495, 1975) spawned a revolution in biology equal in impact to that from the invention of recombinant DNA cloning. Monoclonal antibodies produced from hybridomas are already widely used in clinical and basic scientific studies. Applications of human B cell hybridoma-produced monoclonal antibodies hold great promise for the treatment of cancer, viral and microbial infections, B cell immunodeficiencies with diminished antibody production, and other diseases and disorders of the immune system.
Unfortunately, a number of obstacles exist with respect to the development of human monoclonal antibodies. This is especially true when attempting to develop monoclonal antibodies which define human tumor antigens for the diagnosis and treatment of cancer. Many of these tumor antigens are not recognized as foreign antigens by the human immune system, therefore, these antigens may not be immunogenic in man. By contrast, those human tumor antigens which are immunogenic in mice can be used for the production of mouse monoclonal antibodies that specifically recognize the human antigen and which may be used therapeutically in humans. However, repeated injections of "foreign" antibodies, such as a mouse antibody, in humans, can lead to harmful hypersensitivity reactions as well as increased rate of clearance of the circulating antibody molecules so that the antibodies do not reach their target site.
Another problem faced by immunologists is that most human monoclonal antibodies obtained in cell culture are of the IgM type. When it is desirable to obtain human monoclonals of the IgG type, however, it has been necessary to use such techniques as cell sorting, to identify and isolate the few cells which are producing antibodies of the IgG or other type from the majority producing antibodies of the IgM type. A need therefore exists for an efficient method of switching antibody classes, for any given antibody of a predetermined or desired antigenic specificity.
The present invention bridges both the hybridoma and genetic engineering technologies to provide a quick and efficient method, as well as products derived therefrom, for the production of a chimeric human/non-human antibody.
The chimeric antibodies of the present invention embody a combination of the advantageous characteristics of monoclonal antibodies derived from mouse-mouse hybridomas and of human monoclonal antibodies. The chimeric monoclonal antibodies, like mouse monoclonal antibodies, can recognize and bind to a human target antigen; however, unlike mouse monoclonal antibodies, the species-specific properties of the chimeric antibodies will avoid the inducement of harmful hypersensitivity reactions and will allow for resistance to clearance when used in humans in vivo. Moreover, using the methods disclosed in the present invention, any desired antibody isotype can be conferred upon a particular antigen combining site.